He isn’t coming to the Democratic National Convention but is spending the week in New York City, anchoring coverage of the event for his network Current TV.

Gore's evolution over the past four years — from a central figure in the Democratic Party to a no-show at its biggest event — matches what has happened to the issue of climate change itself, which moved to the sidelines alongside its chief crusader, environmentalists and some Democrats say.

It’s not like Gore hasn’t noticed — and his frustration with Obama has been on display. He’s leveled criticism at Obama for abandoning the push for a climate change bill. He accused him of failing to use the bully pulpit to spread the word about the dangers of rising global temperatures. And he faulted Obama for putting off tough new smog regulations.

On the other hand, Gore has also offered some defense of Obama’s record and says that “I would fear for the future of our environmental policy” if Mitt Romney wins the election.

People who know Gore say this is the role where he feels he can make a difference now — critic and outsider, more activist than politician.

“He is not someone who is inside the system right now,” said Chris Lehane, a political consultant who worked in the Clinton White House and later on Gore’s 2000 presidential campaign. “He is someone that recognizes that ... you need someone who is a critical voice and picks and chooses when he needs to push.

“He’s obviously a Democrat and will always be a Democrat,” Lehane added. “But he’s spent an awful lot of time engaging in activities that are above and beyond partisan politics.”

While many Democrats in Charlotte were reluctant to talk about Gore for attribution, some said Gore's diminished profile — and the environmental movement’s more broadly — is rooted in the mood of a country preoccupied with questions about the economy and jobs.

“Al Gore has proven incapable of developing policies that have broad political appeal, and the party is looking to others,” said Paul Bledsoe, who was communications director for the White House Climate Change Task Force under President Bill Clinton and is now a senior adviser at the Bipartisan Policy Center.

Carl Pope, who served as the executive director of the Sierra Club for almost 20 years, also sees the shift in Gore’s role, especially as prospects for Congress to act on climate change have dimmed.

“Like all of us, I think, Gore is in the process of testing and figuring out what the best pathway forward is,” Pope said. “He sees that the public arena is at the moment more critical than the political arena.”

It’s unclear whether Gore wanted a role this year at the convention. He announced plans to anchor Current TV’s convention coverage from New York before organizers finished sending their speaker invitations.

Aside from any differences with the administration on policy, some events in the former vice president’s personal life may have made him less than ideal for prime time exposure in Charlotte. They include his separation from his wife, Tipper, and the unproven assault allegations that authorities in Portland, Ore., cleared him of two years ago.

But his outside role is a contrast to the prominent speaking slot Obama has granted to Clinton, who serves to remind voters of the prosperous economy that reigned during the last Democratic administration.

As for the relative quiet on climate change, Sen. Sheldon Whitehouse faults his own party, saying Democrats have allowed the GOP to intimidate them from talking up the issue.

“I think the Republicans do a very good propaganda job of poisoning certain phrases. And then, rather than fight, we walk a step back, and we use a different phrase,” said the Rhode Island Democrat, who didn’t address questions about Gore specifically. “Once they poison that phrase, we’ll walk back again. So, we say: ‘We won’t talk about climate change anymore. Now we’re going to talk about clean energy.’”

Four years ago, Gore had a starring role on the final night in the 75,000-capacity stadium in Denver, where he was one of the last few speakers chosen to stir up the crowd before Obama’s acceptance speech.

Gore himself was coming off a year of triumphs, including his Nobel Peace Prize and the Oscar awarded to his global-warming documentary “An Inconvenient Truth.” And he assured voters Obama would take action on the issue that George W. Bush had neglected.

“We are facing a planetary emergency, which, if not solved, would exceed anything we've ever experienced in the history of humankind,” Gore said. Obama, he promised, would offer “solutions for the climate crisis.”

Obama himself had stoked such hopes earlier in the 2008 campaign, famously promising at one point that “this was the moment when the rise of the oceans began to slow and our planet began to heal.”

But this time around, climate change has all but disappeared from Obama’s campaign rhetoric, although his recent speeches have included a line that “denying climate change won't make it stop” and climate remains part of the DNC platform.